This is reproducible using eclipselink 2.3.3 and 2.4.0 and 2.4.1, did not try any other versions. Our application is deployed on WLS 10.3.4 and uses Spring 3.1 with the JpaTransactionManager. It is not related to a particular JPA entity, whatever the use case is we're executing - if it is the first time that a JPA entity needs to be saved we get the exception. After this first time everything works as normally.

If there is anything i can do to provide more debug info for this let me know, it's perfectly reproducible. The only thing i cannot provide easily is an isolated testcase.